The present invention generally relates to devices which control the velocity of high-pressure fluids and, more particularly, to such devices which include a stack of labyrinth discs or valve trim.
Valves or other throttling devices, that is devices having an orifice with a high velocity short throat section, are typically utilized in controlling the flow of high-pressure fluids. These devices, however, are typically subject to severe cavitation, noise, vibration, and erosion problems. Fluid in a liquid state may vaporize as it passes through the throat section of the orifice and then recondense downstream with implosive action which induces high energy shock waves. The shock waves can severely damage and/or erode sections of the valve or pipe. Compressible fluids, or fluids in a gaseous state, have extremely high velocities when subjected to high pressure drops across a short throat section. Such high velocities cause fluid turbulent interaction which results in unacceptable levels of noise and vibration.
It is well established that limiting kinetic energy exiting the throttling area, reduces problems of noise, vibration, erosion, and shortened product life. Therefore, many fluid control devices include restrictors which dissipate energy in conjunction with fluid throttling. The most common restrictors subdivide the flow into a plurality of small, long, and tortuous serpentine or labyrinth passageways with abrupt turns. Energy is dissipated through either frictional resistance, multiple changes of direction created by either baffles or obstructions, or a combination of both. By providing such energy dissipation methods to sufficiently reduce the pressure, while expanding the area of the passageway, the velocity of the fluid is controlled to within acceptable limits.
In fluid control valves, the tortuous passageways are usually incorporated in valve trim. Typically, a valve plug is surrounded with a stack of annularly-shaped discs, forming a cylinder. These fluid control valves, however, can still have relatively high levels of noise, vibration, and erosion. This is believed to be due to the fact that the devices do not behave as theoretically predicted. There is actually very little frictional loss because the fluid tends to take the path of least resistance. That is, the fluid tends to hug the ends of projections, creating dead zones in the corners, resulting in a much less tortuous path than one would imagine by simply looking at the disc passageways. Additionally, the pressure profile from the inlet to the outlet is often nonlinear and unpredictable. Accordingly, there is a need in the art for an improved high-energy loss fluid control device which increases product life, has a relatively linear and predictable pressure profile, and reduces noise, vibration, and erosion.